70mm Insulation Board

A 70mm insulation board is used when a building needs a significant increase in thermal performance, but space is limited.

At this thickness, the board provides a measurable reduction in heat transfer through walls, roofs, or floors.

What is 70mm thick insulation board?

A 70mm thick insulation board is a rigid slab designed to reduce heat transfer in a building through conduction and convection.

The “70mm” refers to its depth, which is thick enough to noticeably reduce heat loss while still fitting within common wall, floor, and roof build-ups used on site.

The board is dimensionally stable and can fit tightly against structural elements without slumping or compressing over time.

What is 70mm insulation thickness board used for?

70mm insulation thickness boards are used:

• In pitched roofs between and over rafters to reduce heat loss through the roof.
• Under floors or in floor screeds to reduce heat loss downwards.
• Inside cavity walls where cavity width allows or between studs, to boost wall thermal resistance.
• In ceilings or lofts to help keep upstairs rooms warm.

Because it is rigid, the board supports itself and sits flush with framing, helping contribute towards building energy performance requirements without adding too much bulk.

Types of 70mm insulation board

70mm insulation boards are available in the following material types:

PIR Insulation (Polyisocyanurate)

These are the most common. They have a rigid foam core with reflective foil facings that help trap heat. PIR boards give strong thermal performance for their thickness (around 0.022 W/m.K), allowing target U-values to be achieved with reduced build-up depth.

Phenolic Insulation Foam Board

Phenolic boards have a foam core that is made from phenolic resin. Their lambda value is around 0.021 W/m.K, with 70mm phenolic insulation boards delivering reliable performance where space is limited, and high thermal performance is required.

EPS Insulation (Expanded Polystyrene)

EPS is a bead-based foam that is easy to cut. It has higher conductivity (less insulating per millimetre) than PIR/phenolic, but it’s useful where cost matters and the performance requirements are lower. It is sometimes used beneath screeds and in external render systems.

Benefits of insulation 70mm thickness board

Using a 70mm rigid insulation board offers advantages like:

• Thermal efficiency – It resists heat flow well for its size, helping rooms stay warm with less energy.
• Slim build-ups – A 70mm insulation thickness board fits in common timber depths and tight spaces without needing larger structures.
• Rigid and neat – Boards cut cleanly, install flush with studs or joists, and reduce unwanted gaps that reduce thermal performance.
• Versatile – For many wall and roof build-ups, 70mm fits naturally within the structure without forced design changes.
• Long-lasting – Rigid 70mm materials do not sag or settle like soft insulation can over time.